The studies outlined in this proposal use Drosophila to determine the role of proteins that cooperate with actin to mediate the actin cytoskeleton's participation in normal cell physiology. In particular, the role of this cytoskeletal system in dynamic processes that are important for development of the organism will be examined. The focus of this proposal is an novel unconventional myosin, called the Drosophila 95F unconventional myosin, that is present (in most if not all cells) throughout the life cycle of the fly. Evidence suggests that it plays an important role in early development of the embryo. To examine the function of this protein during the life cycle of Drosophila, the studies to be performed utilize a variety of tools available in this model organism. Primarily, the effects of mutation in the gene that encodes this myosin heavy chain will be analyzed to determine when and in which tissues this protein plays a role. In addition, biochemical properties of the protein will be examined, using in vitro assays for function, in vivo techniques for visualization of processes in which this protein participates, and disruption of function using antibodies and other reagents. The myosin family of mechanochemical enzymes contains a diverse group of proteins that are thought to mediate a variety of important cellular dynamic processes. However, the particular role of each of the many different members of the family remains unclear. It is likely the experiments proposed in this application will provide information on the particular role of this myosin in a variety of tissues and at different stages of organism development; thus, these experiments will provide significant insight into how cells participate in organism function, as well as to provide information on the particular actin-based process required in different cells for their normal function.